This invention relates to improvements in or relating to cooling devices for electric rotary machines, and more particularly it is concerned with a cooling device for an electric rotary machine of the type including a water-wheel generator which has salient poles.
As is well known, an electric rotary machine of the salient-pole type popularly used nowadays in formed with a yoke rotating with the rotary shaft and having a plurality of salient poles affixed to its outer periphery and varying in number depending on the number of poles. Generally, the salient poles rotate within the stator.
It is not too much to say that the output power of an electric rotary machine may generally vary depending on the maximum temperature at heat generating sections of the machine, particularly the portions of the stator and rotor in which coils are disposed. Thus, an electric rotary machine of the aforementioned type is provided with a cooling device therefor.
In an electric rotary machine of the type described, heat is usually generated in field coils wound on the salient poles and stator coils. It is usual practice to cause a stream of cooling gas to move through the portions in which these coils are disposed to effect cooling.
It may seem easy to cause streams of cooling gas to move through heat generating portions, but the problem involved is not so simple as it seems. If the heat generating portion were disposed in the center of a large space, it would be easy to select as desired the volume of gas used and the directions in which the streams of gas are directed. What is important is to effect cooling with the highest degree of efficiency by utilizing a small space and a limited paths for the movement of the streams of cooling gas. Thus, cooling of an electric rotary machine of the type described poses a problem difficult to obviate in actual practice.
An example of the cooling device now in use which is considered to operate with the highest degree of efficiency with a machine of the medium capacity will be described first of all. Such cooling device is provided with a radial fan mounted at each axial end of the yoke of the rotor for supplying a stream of cooling gas used to cool the coils of the stator. On the other hand, coils wound on the poles of the rotor are cooled either by streams of gas discharged through gas passageways disposed between the poles and formed in the yoke or by a portion of the streams of gas produced by each fan which is caused to move axially between the adjacent poles.
The coils of the rotor and the stator can be cooled sufficiently to enable the machine to operate without failure by the aforementioned arrangement if the electric rotary machine is of a small or medium capacity. If the machine is 500 MVA or a greater capacity which has come to be used widely in recent years, however, the amount of heat generated in the machine increases and the volume of cooling gas required increases in proportion to the increase in the capacity of the machine.
It is not easy to increase the volume of cooling because the space employed for cooling must be increased. An increase in the capacity of an electric machine does not necessarily entail an increase in the space available for effecting cooling. Besides, an increase in the volume of cooling gas causes the production of a windage loss and a noise, which is not desirable in increasing the capacity of an electric rotary machine.
Cooling of the stator coils (coil ends) can be effected relatively easily beacuse they are disposed in a relatively large space. If a sufficiently large volume of gas to cool the coils wound on the poles is caused to flow between the adjacent poles, it will be possible to cool the poles but there will be an increase in the overall volume of gas used, thereby causing the production of an windage loss or a noise as aforementioned.